1. Field of the Invention
The present invention relates to an ink tank, an ink tank-integrated head cartridge constructed of the ink tank and an ink head integrated with the ink tank, and an ink jet printing apparatus having the ink tank or the head cartridge, and more particularly, to an improved construction with an absorbing member for holding ink provided in the ink tank. Here, printing refers to processes involving the imparting of ink to any of ink supports to be inked, such as cloth, yarn or sheet materials. The present invention can be used for all information processing devices, or instruments including printers as their output devices.
2. Description of the Related Art
Of print heads of the ink jet type, a print head is known to have heating elements and eject a printing liquid such as ink (hereinafter referred to as ink) by utilizing thermal energy generated by the heating elements. In the print head, the heating elements or ink orifices can be miniaturized. Thus, the use of a print head of this type permits the printing of highly accurate images. This type of ejection also enables relatively high speed and low noise printing.
In addition to the above-described advantages, this type of print head can be produced by the same film forming step as for a semiconductor device, so that its price can be rendered relatively low. Hence, a proposal has been made of a head cartridge constructed of such a print head and an ink tank integrated with the print head and being attachable to and detachable from the apparatus. With such a construction, it becomes possible to replace the ink tank together with the print head by a new head cartridge when the ink in the ink tank has been used up.
In such a head cartridge, fresh ink in an amount corresponding to the amount of ink consumed by the print head needs to be fed to the print head through a feed port from a liquid reservoir serving as an ink tank for holding ink. Furthermore, when ink need not be fed because no printing is done, ink is required not to leak from the feed port to the outside of the reservoir.
Such a requirement is important for the above reservoir used in the ink jet system of the kind performing printing by ejecting ink from the print head, particularly in consideration of the possible influence of the feed amount of ink on image quality. As ink tanks fulfilling that requirement, the forms described below have been heretofore known.
FIG. 1 is a sectional view illustrating the internal structure of an ink tank in a head cartridge for use in a conventional ink jet printing apparatus. In FIG. 1, the reference numeral 311 denotes a cartridge body. The cartridge body 311 has in its inside an ink tank, which houses almost throughout it an absorbing member 312 for holding ink. In a side wall of the cartridge body 311 is provided an ink supply port 313 for making the inside of the ink tank communicating with a print head (not shown). In another side wall of the cartridge body 311 is formed an air communicating port which enables communication between the inside of the cartridge body 311 and the atmosphere. In FIG. 1, the symbol a represents that portion of the absorbing member 312 which holds ink, and the symbol b represents that portion of the absorbing member 312 which does not hold ink.
With the cartridge of the above construction, negative pressure within the ink reservoir is controlled by the capillary force of the absorbing member 312, and thus causes no ink leakage to the outside.
The use, say, of a urethane foam as a constituent of the absorbing member 312, however, poses the following two problems, making it practically impossible to detect the amount of ink remaining in the cartridge with the naked eye or by an optical means:
First, the change in the reflection density of the absorbing member 312 depending on the presence or absence of ink in the absorbing member is small, thus making the boundary between the portion a and the portion b in FIG. 1 not clearly visible.
Secondly, the long-term storage of the cartridge results in the yellowing of the absorbing member 312 itself, causing a marked change in its reflection density. In the case of yellow ink, in particular, the difference between the density before and after consumption of ink is 0.1, making it virtually impossible to optically detect the amount of ink that has remained.
A known example of a remaining ink amount detection means in an ink tank using such an absorbing member is that of the construction described in U.S. Pat. No. 5,079,570.
FIGS. 2A and 2B are sectional views showing the construction of a head cartridge having a remaining ink amount detection means disclosed in this patent. FIG. 2A shows the absorbing member filled up with ink, and FIG. 2B shows the consumption of ink proceeding. In FIGS. 2A and 2B, the numeral 210 denotes a head cartridge using an absorbing member. The cartridge 210 is composed of a housing 212, an absorbing ink reservoir 214 for storing a large amount of ink therein, a C-letter shaped transparent tube 220 for detection of an ink level, and a print head 216. The C-letter shaped transparent tube 220 is composed of a transparent central tubular portion 220a which is disposed so as to extend in a vertical direction (gravitational direction) when the head cartridge 210 is placed in the same posture as during use and which indicates the position of the ink level to the outside; and an upper tubular portion 220b and a lower tubular portion 220c which are connected to the ends of the central tubular portion 220a and supply ink to the tubular portion 220a.
In the cartridge of the above construction, however, when the level of ink held in the absorbing member within the housing 212 lowers to below the upper tubular portion 220b as shown in FIG. 2B as a result of increasing consumption of ink, ink within the central tubular portion 220a and the lower tubular portion 220c is absorbed to the absorbing member side under the capillary action of the absorbing member. Consequently, all the ink in the C-letter shaped transparent tube 220 is exhausted, indicating no ink remaining. That is, the C-letter shaped transparent tube 220 indicates ink exhaustion, although there is a considerable amount of ink held in the portion a of the absorbing member.
The cartridge of the above construction also requires a step of attaching the C-letter shaped transparent tube 220 to the housing 212, thus adding to costs.
Furthermore, if there is a member for supplying ink held in the absorbing member to the print head 216 upon contact with the absorbing member at a point near the ink outlet inside the housing 212 corresponding to the position of the print head 216, this contact may bring about the deterioration of the absorbing member over time, forming voids there and exerting adverse influences from the dwelling of air. In the worst case, communication between the air communicating port 217 and the voids near the ink outlet may emerge. This may make the desired ejection impossible, and cause ink existent in the ink supply passage to drool from the ink ejection orifice, thereby staining the inside of the apparatus, etc.
In addition, ink supply from the absorbing member to the ink outlet relies on the action of gravity, and so may fail to accompany the driving of the print head, etc. at a high frequency which has recently been desired. In order to enhance the accompanying characteristic of ink supply, it is conceivable to give a certain large bore diameter to the ink orifice of the print head, thereby lowering the resistance of flow through the ink supply passage leading to the ink orifice. In this case, the ink retaining capacity of the absorbing member may lower, and ink leakage from the air communicating port may occur.
U.S. Pat. No. 4,929,969 describes in column 7, lines 52-57 that compression may be desired in particular applications to adjust structural interstitial spaces, while maintaining the useful or preferred characteristics in an incompressed state.